24 Day Core Challenge The B.Nick Fitness 24-Day Ab Challenge is designed to specifically tone, strengthen and boost your core muscles to the max. The challenge consists of 4 different exercises which are required daily. The time spent doing the exercises slowly increases day by day, to help build up your body's core strength gradually, ensuring you are able to complete the final day of the challenge with ease. You are only required to complete the number of reps shown on the 24-Day Ab Challenge chart once per day; however if you are feeling brave, you can repeat each day's challenge as many times as you'd like. Keep in mind, by day 24 it will be very difficult to complete multiple times.